I have 400 hours across TWH2 and TWH3, including Ku'gaths campaign, and I gotta say Kairos is the first campaign that I have no idea how to survive. Despite being a strong lord once leveled-up, Kairos is painfully weak as a faction, and it hurts his campaign. I've seen some people defend Kairos is in a good spot (probably because AI Kairos tends to dominate the southern Southlands and he is a very strong lord), but I want you to play a Hard/Very Hard campaign with him and come back after you've gotten his Short Victory. These are my main gripes with Kairos.
1) Lorewise, it is questionable that Tzeentch actually acknowledges Vilitch's existence, yet he has much more potential using Tzeentch faction mechanics in Immortal Empries than Kairos, Tzeentch's own freaking advisor.
Vilitch starts with all of his his Changing of the Ways abilities unlocked except for one, while Kairos needs to research virtually every single one of his Changing Ways while paying Grimoires to do so. Also, Vilitch's Changing Ways abilities are cheap enough to use from turn one onwards. Kairos' Changing requires prohibitively expensive grimoire costs for abilities that aren't even that good compared to Vilitch's. Giving Kairos Spawnify alone would give him a valuable tool to fight the factions around him.
2) Kairos' abilities are pathetic compared to the factions around him.
Yes, alone as a lord he is very strong, but with such an indefensible position in the Southern Chaos Wastes he cannot be everywhere at once, and his auxilary armies are not equipped to fight the factions around him. Teclis has access to many lores of magic just like Kairos, but his missile units and infantry are worlds better than anything Kairos could field at that same stage of the game. Slaanesh hard-counters Tzeentch units by being fast and high-damaging. Oxyotl can summon entire stacks of late-game monsters using the Rite of Primeval Glory, while Kairos' economy can barely afford an army or two of marauders and blue/pink horrors and maybe a couple of Screamers of Tzeentch. Half the time Kairos cannot even use his abilties because he needs so many grimoires just to perform actions like causing a rebellion, which never practically does any sort of value whatsoever. I really think lowering the cost of his Changing Ways or increasing the grimoires gained post-battle will make Changing Ways at least somewhat impactful for him for more than 1 turn for the entire early-game.
3) Relying on ambush stance is not a good game mechanic.
Yes, Kairos has very good ambush chances and teleport stance, but you cannot teleport on enemy armies every time you see a stack that is going to deal heavy losses to you, not to mention the AI does a really good job at staying just far enough to be out of teleport range. Using regular ambush stance is relying mostly on RNG and hoping the AI doesn't park an agent next to your army and foiling your ambush anyways. Using your own heroes to wound/assasinate theirs is also completely RNG based and could potentially lead to the loss of your hero during a critical failure, in which you most-likely have no buildings to recruit them back. He either needs the economy for more armies or stronger units. I would personally prefer more money for armies. Besides, one of his faction effects are literally -50% battle reinforcement time. This is literally useless for 80% of the game when Kairos can barely afford enough armies to get okay-ish defense over his starting territory.
I really like Kairos and Tzeentch in general, but I just find more suffering than fun in his campaign.